Technical Abstract:
A shipment of beans from the U.S. northern plains region was found to contain unacceptable levels of ochratoxin-A (OA) at processing time. One hundred and twenty-one beans were removed from a sample and soaked in ca 250 mL of 2% sodium hypochlorite solution for 5 minutes with occasional agitation. The sodium hypochlorite solution was decanted and ca. 250 mL of sterile distilled water was added and gently agitated for 5 minutes. The rinse water was decanted and discarded. Individual beans were placed on Czapek’s agar. In half of the samples, the Czapek’s agar was supplemented with 0.01% chlorotetracycline and 0.01% penicillin-G to reduce bacterial contamination. Beans were incubated in darkness at 25 deg. C and examined using a dissecting microscope at days 5 and 10. Fungi from the beans were transferred with a sterile wire needle to Czapek’s agar tubes for growth and identification.
Identification was made on seven day old cultures incubated under standard conditions on standard media. Nearly half of the beans examined were free of any fungal growth. Most common infestations were by Eurotium species, E. amstellodami, E. repens and E. rubrum. The Eurotium species are adapted to very dry habitats and substrates and while they are known to produce secondary metabolites, they are not OA producers. The Penicillium species included P. citrinum, P. aurantiogriseum, P. polonicum and P. verrucosum. The latter species is capable of producing OA. Aspergillus ostianus was found in nearly 10% of beans and is from the A. ochraceus group. While there have been reports that it produces OA, it is doubtful whether this species actually produces OA. A single isolate of Aspergillus niger was found on beans and only a low percentage of A. niger isolates produce OA. It seems likely the source of OA contamination was exogenous to the beans.